A conventional uninterruptible power supply device includes a converter, an inverter, and a bypass circuit. In normal times in which AC power is supplied normally from an AC power supply, AC power supplied from the AC power supply is converted into DC power by the converter, and then, the DC power is stored in a power storage device and is also converted into AC power by the inverter, and the AC power is supplied to a load. If the inverter has failed, the AC power from the AC power supply is supplied via the bypass circuit to the load. In a power failure in which a supply of the AC power from the AC power supply is stopped, the DC power of the power storage device is converted into AC power by the inverter, and the AC power is supplied to the load (for example, see Japanese Patent Laying-Open No. 2010-220339 (Patent Document 1)).